This invention is directed to a method for increasing retention and drainage in a papermaking furnish using structurally rigid polymeric coagulants in combination with a flocculant and a microparticle.
In the manufacture of paper, a papermaking furnish is formed into a paper sheet. The to papermaking furnish is an aqueous slurry of cellulosic fiber having a fiber content of about 4 weight percent (percent dry weight of solids in the furnish) or less, and generally around 1.5% or less, and often below 1.0% ahead of the paper machine, while the finished sheet typically has less than 6 weight percent water. Hence the dewatering and retention aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
Gravity dewatering is the preferred method of drainage because of its relatively low cost. After gravity drainage more expensive methods are used for dewatering, for instance vacuum, pressing, felt blanket blotting and pressing, evaporation and the like. In actual practice a combination of such methods is employed to dewater, or dry, the sheet to the desired water content. Since gravity drainage is both the first dewatering method employed and the least expensive, an improvement in the efficiency of this drainage process will decrease the amount of water required to be removed by other methods and hence improve the overall efficiency of dewatering and reduce the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency and cost is retention of furnish components on and within the fiber mat. The papermaking furnish represents a system containing significant amounts of small particles stabilized by colloidal forces. The papermaking furnish generally contains, in addition to cellulosic fibers, particles ranging in size from about 5 to about 1000 nm consisting of, for example, cellulosic fines, mineral fillers (employed to increase opacity, brightness and other paper characteristics) and other small particles that generally, without the inclusion of one or more retention aids, would in significant portion pass through the spaces (pores) between the mat formed by the cellulosic fibers on the papermachine.
Greater retention of fines, fillers, and other components of the furnish permits, for a given grade of paper, a reduction in the cellulosic fiber content of such paper. As pulps of lower quality are employed to reduce papermaking costs, the retention aspect of papermaking becomes more important because the fines content of such lower quality pulps is generally greater. Greater retention also decreases the amount of such substances lost to the whitewater and hence reduces the amount of material costs, the cost of waste disposal and the adverse environmental effects therefrom. It is generally desirable to reduce the amount of material employed in a papermaking process for a given purpose, without diminishing the result sought. Such add-on reductions may realize both a material cost savings and handling and processing benefits.
An important method of enhancing dewatering while improving the retention of cellulosic fines, mineral fillers and other furnish components on the fiber mat employs an inorganic microparticle in combination with a coagulant and a polymeric flocculant. In such a system a coagulant is first added, followed by the flocculant and the microparticle.
The coagulant is generally a low molecular weight synthetic cationic polymer or cationic starch. The coagulant may also be an inorganic coagulant such as alum or polyaluminum chlorides. The coagulant addition can take place at one or several points within the furnish make up system, including but not limited to the thick stock, white water system, or thin stock of a machine. The coagulant generally reduces the negative surface charges present on the particles in the furnish, such as cellulosic fines and mineral fillers, and thereby accomplishes a degree of agglomeration of such particles. Further, in the presence of other detrimental anionic species, the coagulant serves to neutralize the interfering species enabling aggregation with the subsequent addition of a flocculant.
The flocculant generally is a high molecular weight synthetic polymer which bridges the particles and/or agglomerates, from one surface to another, binding the particles into larger agglomerates. The presence of such large agglomerates in the furnish, as the fiber mat of the paper sheet is being formed, increases retention. The agglomerates are filtered out of the water onto the fiber web, whereas unagglomerated particles would, to a great extent, pass through such a paper web. In such a program the order of addition of the microparticle and flocculant can be reversed successfully.
However, there is continuing need to develop improved agents for improving the retention and drainage performance of the papermaking furnish, thereby increasing the efficiency of pulp or paper manufacture.
Structurally rigid polymers have been used as substitutes for pulp in papermaking (U.S. Pat. No. 4,749,753; Japanese Patent Application 1987-29251), but not as process additives. We have discovered that adding structurally rigid polymeric coagulants to papermaking furnishes results in a substantial improvement of the retention and drainage properties of the furnishes.
Accordingly, in its principal embodiment, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish an effective amount of a structurally rigid polymeric coagulant and an effective flocculating amount of a flocculant and a microparticle.
Definitions of Terms
xe2x80x9cStructurally rigid polymersxe2x80x9d means polymers having a structure where the rotational conformation (degrees of freedom) of the polymer are restricted compared with common flexible polymeric materials. Structural rigidity is imparted to the polymeric coagulants described herein by incorporating rigid components such as alkenyl, alkynyl, cyloalkyl, heterocyclyl, aryl and heteroaryl groups along the main chain of the polymer. The structurally rigid polymers may be composed entirely of rigid components, or the rigid components may be connected by flexible chains such as alkyl or ether groups, so long as introduction of the flexible groups does not substantially effect the overall rigidity of the polymer. Further, the structurally rigid polymers should be water-soluble or water-dispersable and have cationic charge.
xe2x80x9cCyclic ditertiary aminexe2x80x9d means an aromatic or aliphatic monocyclic or multicyclic ring system of formula 
where xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d denote, respectively, a monocyclic, bicyclic or fused aromatic or aliphatic ring system of from about 5 to about 10 ring atoms and R9 and R10 are alkyl of from one to about 4 carbon atoms. The nitrogen atoms are separated by at least one ring atom, preferably by at least two ring atoms. Where the cyclic ditertiary amine is aliphatic, the nitrogen atoms are further substituted with alkyl. Preferably, the alkyl groups are connected to form a bridged heterocylic ring. The cyclic ditertiary amine is optionally substituted with one or more substituents selected from alkyl, alkoxy and haloalkyl. Preferred cyclic ditertiary amines are 1,4-diazabicyclo[2.2.2]octane, 4,4-dipyridine, pyrazine and 1,4-dimethylpiperazine. A more preferred cyclic ditertiary amine is 1,4-diazabicyclo[2.2.2]octane.
xe2x80x9cAcyclic ditertiary aminexe2x80x9d means an amine of formula 
where R1-R4 are alkyl and L1 is C1-C6 alkylene, C2-C6 alkenylene, C2-C6 alkynylene, arylene, heteroarylene heterocycylene or cycloalkylene. Preferred acyclic ditertiary amines are N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-2-butene-1,4-diamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyldiaminomethane, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-2,2-diaminopropane and N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,4-diaminocyclohexane. N,N,Nxe2x80x2,Nxe2x80x2-Tetramethyl-1,4-diaminocyclohexane is more preferred.
xe2x80x9cCyclic dihalidexe2x80x9d means an aliphatic cylcoalkyl of formula 
where xe2x80x9cCxe2x80x9d denotes a cycloalkyl of from about 5 to about 10 carbon atoms and X is halogen. The halogen-substituted carbon atoms are separated by at least one carbon atom, preferably by at least two carbon atoms. The cyclic dihalide is optionally substituted with one or more substituents selected from alkyl, alkoxy and haloalkyl. A preferred cyclic dihalides is 1,4-dichlorocyclohexane.
xe2x80x9cAcyclic dihalidexe2x80x9d means dihalide of formula 
where X is halogen, L2 is C2-C6 alkylene, C2-C6 alkenylene, C2-C6 alkynylene, arylene, heteroarylene heterocycylene or cycloalkylene and R5-R8 are independently selected from hydrogen and alkyl. Preferred acyclic dihalides are 1,4-dichloro-2-butyne, trans-1,4-dichloro-2-butene, xcex1,xcex1xe2x80x2-dichloro-p-xylene and 1,3-dichloro-2,2-dimethylpropane. A more preferred acyclic dihalide is 1,4-dichloro-2-butyne.
xe2x80x9cAlkylxe2x80x9d means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, and the like.
xe2x80x9cAlkylenexe2x80x9d means a divalent group derived from a straight or branched chain saturated hydrocarbon by the removal of two hydrogen atoms. Representative alkylene groups include methylene, ethylene, propylene, and the like.
xe2x80x9cAlkenylenexe2x80x9d means a divalent group derived from a straight or branched chain hydrocarbon containing at least one carbon-carbon double bond. Representative alkenylene include xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CH2CHxe2x95x90CHxe2x80x94, xe2x80x94C(CH3)xe2x95x90CHxe2x80x94, xe2x80x94CH2CHxe2x95x90CHCH2xe2x80x94, and the like.
xe2x80x9cAlkynylenexe2x80x9d means a divalent group derived by the removal of two hydrogen atoms from a straight or branched chain acyclic hydrocarbon group containing a carbon-carbon triple bond. Representative alkynylene include xe2x80x94CHxe2x89xa1CHxe2x80x94, xe2x80x94CHxe2x89xa1CHxe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x89xa1CHxe2x80x94CH(CH3)xe2x80x94, and the like.
xe2x80x9cAlkoxyxe2x80x9d and xe2x80x9calkoxylxe2x80x9d mean an alkyl-Oxe2x80x94 group wherein alkyl is defined herein. Representative alkoxy groups include methoxyl, ethoxyl, propoxyl, butoxyl, and the like.
xe2x80x9cArylxe2x80x9d means an aromatic monocyclic or multicyclic ring system of about 6 to about 20 carbon atoms, preferably of about 6 to about 10 carbon atoms. The aryl is optionally substituted with one or more alkyl, alkoxy or haloalkyl groups. Representative aryl groups include phenyl or naphthyl, or substituted phenyl or substituted naphthyl.
xe2x80x9cArylenexe2x80x9d means a divalent group derived from an aryl as defined herein by the removal of two hydrogen atoms, provided that in no cases are the hydrogen atoms on adjacent carbon atoms.
xe2x80x9cCycloalkylxe2x80x9d means a non-aromatic mono- or multicyclic ring system of about 5 to about 10 carbon atoms. Preferred ring sizes of rings of the ring system include about 5 to about 6 ring atoms. The cycloalkyl is optionally substituted with one one or more substituents selected from alkyl, alkoxy and haloalkyl. Representative monocyclic cycloalkyl include cyclopentyl, cyclohexyl, cycloheptyl, and the like. Representative multicyclic cycloalkyl include 1-decalin, norbornyl, adamant-(1- or 2-)yl, and the like.
xe2x80x9cCycloalkylenexe2x80x9d means a divalent group derived from a cycloalkyl as defined herein by the removal of two hydrogen atoms, provided that in no cases are the hydrogen atoms on adjacent carbon atoms.
xe2x80x9cHeteroarylxe2x80x9d means an aromatic monocyclic or multicyclic ring system of about 5 to about 10, preferably from about 5 to about 6 ring atoms, in which one or more of the atoms in the ring system is/are element(s) other than carbon, for example nitrogen, oxygen or sulfur. The heteroaryl is optionally substituted with one one or more substituents selected from alkyl, alkoxy and haloalkyl. Representative heteroaryl groups include pyridyl, quinolyl, furyl, benzofuryl, thienyl, thiazolyl, pyrimidyl, indolyl, and the like.
xe2x80x9cHeteroarylenexe2x80x9d means a divalent group derived from a heteroaryl as defined herein by the removal of two hydrogen atoms, provided that in no cases are the hydrogen atoms on adjacent ring atoms.
xe2x80x9cHeterocyclylxe2x80x9d means a non-aromatic saturated monocyclic or multicyclic ring system of from about 5 to about 10 ring atoms, in which one or more of the atoms in the ring system is/are element(s) other than carbon, for example nitrogen, oxygen or sulfur. Preferred ring sizes of rings of the ring system include about 5 to about 6 ring atoms. The heterocyclyl is optionally substituted by one or more alkyl, alkoxy or haloalkyl groups. Representative heterocyclyl rings include piperidyl, pyrrolidinyl, piperazinyl, morpholinyl, thiomorpholinyl, thiazolidinyl, 1,3-dioxolanyl, 1,4-dioxanyl, tetrahydrofuranyl, tetrahydrothiophenyl, tetrahydrothiopyranyl, and the like.
xe2x80x9cHeterocyclylenexe2x80x9d means a divalent group derived from a heterocyclyl as defined herein by the removal of two hydrogen atoms, provided that in no cases are the hydrogen atoms on adjacent ring atoms.
xe2x80x9cHalogenxe2x80x9d and xe2x80x9chaloxe2x80x9d mean fluorine, chlorine, bromine or iodine.
xe2x80x9cHaloalkylxe2x80x9d means an alkyl group, as defined herein, having one, two, or three halogen atoms attached thereto. Representative haloalkyl groups include chloromethyl, bromoethyl, trifluoromethyl, and the like.
xe2x80x9cFlocculantxe2x80x9d means a chemical agent that is added to a papermaking furnish to assist in the agglomeration of small particles and thereby increase the retention and drainage properties of the furnish. The flocculant may be a non-ionic, anionic or cationic polymer having a molecular weight of at least about 500,000, preferably of at least about 1,000,000 and more preferably of at least about 5,000,000. The flocculant may be used in the solid form, as an aqueous solution, as water-in-oil emulsion, or as dispersion in water.
xe2x80x9cNonionic flocculantxe2x80x9d means homopolymers, copolymers or terpolymers and so on of nonionic monomers. Representative nonionic monomers include acrylamide, methacrylamide, N-tertiary butyl acrylamide, N-vinylformamide, N-vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-3-methylpyrrolidone, N-vinypyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-3-methylpyrrolidone, N-vinyl-5-methylpyrirrolidone, N-vinyl-5-phenylpyrrolidone, N-vinyl-2-oxazolidone, N-vinylimidazole, vinylacetate, maleimide, N-vinylmorpholinone, polyethylene oxide (PEO), and the like. Preferred nonionic monomers are acrylamide, methacrylamide and N-vinylformide. Preferred nonionic flocculants are poly(acrylamide), poly(methacrylamide) and poly(N-vinylformamide).
The dosage of nonionic flocculant is preferably from about 0.001 to about 0.5% (as actives) by weight based on total solids in the slurry, more preferably from about 0.003 to about 0.2% and most preferably from about 0.007 to about 0.1%.
xe2x80x9cCationic flocculantxe2x80x9d means any water-soluble polymer of (meth)acrylamide or any water-soluble polymer of N-vinylformamide or related monomers which carries or is capable of carrying a cationic charge when dissolved in water. Representative cationic copolymers of (meth)acrylamide include copolymers of (meth)acrylamide with dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate or methyl chloride, Mannich reaction modified polyacrylamides, diallylcyclohexylamine hydrochloride (DACHA HCI), diallyldimethylammonium chloride (DADMAC), methacrylamidopropyltrimethylammonium chloride (MAPTAC) and allyl amine (ALA).
xe2x80x9cAnionic flocculantxe2x80x9d any polymer comprised of anionic and nonionic monomers means which carries or is capable of carrying a cationic charge when dissolved in water. Representative anionic monomers include acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylamidomethylbutanoic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, allyl sulfonic acid, allyl phosphonic acid, sulfomethylated acrylamide, phosphonomethylated acrylamide and the water-soluble alkali metal, alkaline earth metal, and ammonium salts thereof. The choice of anionic monomer is based upon several factors including the ability of the monomer to polymerize with the desired comonomer, the use of the produced polymer, and cost. A preferred anionic monomer is acrylic acid. Preferred anionic flocculants are copolymers of acrylamide and acrylic acid.
The dosage of anionic flocculant is from about 0.001 to about 1%, preferably from about 0.01 to about 0.5% and more preferably from about 0.02 to about 0.25% by weight based on total solids in the slurry.
xe2x80x9cZwitterionic flocculantxe2x80x9d means a polymer composed from zwitterionic monomers and, possibly, other non-ionic monomer(s). Representative zwitterionic polymers include homopolymers such as the homopolymer of N,N-dimethyl-N-(2-acryloyloxyethyl)-N-(3-sulfopropyl) ammonium betaine, copolymers such as the copolymer of acrylamide and N,N-dimethyl-N-(2-acryloyloxyethyl)-N-(3-sulfopropyl) ammonium betaine, and terpolymers such as the terpolymer of acrylamide, N-vinyl-2-pyrrolidone, and 1-(3-sulfopropyl)-2-vinylpyridinium betaine. The use of zwitterionic flocculants in papermaking is described in U.S. patent application Ser. No. 09/349,054, incorporated herein by reference.
xe2x80x9cMicroparticlexe2x80x9d means highly charged materials that improve flocculation when used together with natural and synthetic macromolecules. They constitute a class of retention and drainage chemicals defined primarily by their submicron size. A three dimensional structure, an ionic surface, and a submicron size are the general requirements for effective microparticles.
Microparticle programs enhance the performance of current retention programs and optimize wet end chemistry, paper quality and paper machine efficiency. Microparticles are not designed to be used as a sole treatment. Rather, they are used in combination with other wet end additives to, improve retention and drainage on the paper machine. Commonly used microparticles include:
i) copolymers of acrylic acid and acrylamide;
ii) bentonite and other clays;
iii) dispersed silica based materials;
iv) colloidal borosilicate; and
v) naphthalene sulfonate/formaldehyde condensate polymers.
Representative copolymers of acrylic acid and acrylamide are described in U.S. Pat. No. 5,098,520, incorporated herein by reference.
Bentonites useful as the microparticle for this process include: any of the materials commercially referred to as bentonites or as bentonite-type clays, i.e., anionic swelling clays such as sepialite, attapulgite and montmorillonite. In addition, bentonites described in U.S. Pat. No. 4,305,781 are suitable. A preferred bentonite is a hydrated suspension of powdered bentonite in water.
Representative dispersed silicas have an average particle size of from about 1 to about 100 nanometers (nm), preferably from about 2 to about 25 nm, and more preferably from about 2 to about 15 nm. This dispersed silica, may be in the form of colloidal, silicic acid, silica sols, fumed silica, agglomerated silicic acid, silica gels and precipitated silicas, so long as the particle size or ultimate particle size is within the above ranges. Dispersed silica in water with a typical particle size of about 4 nm is available from Nalco Chemical Company, Naperville, Ill.
Representative borosilicates are described in Patent Cooperation Treaty Patent Application No. PCT/US98/19339, incorporated herein by reference. Colloidal borosilicate is available from Nalco Chemical Company, Naperville, Ill.
Naphthalene sulfonate/formaldehyde condensate polymers useful as microparticles are available from Nalco Chemical Company, Naperville, Ill.
Other suitable microparticles include the structurally-rigid polymers disclosed in U.S. Patent application Ser. No. 09/740,548 filed concurrently herewith, titled xe2x80x9cStructurally Rigid Nonionic and Anionic Polymers as Retention and Drainage Aids in Papermakingxe2x80x9d, incorporated herein by reference.
The amount of microparticle added is from about 0.05 to about 5.0, preferably from about 1.5 to about 4.5 and more preferably about 2 to about 4.5 pounds microparticle/ton.
xe2x80x9cPounds microparticle/tonxe2x80x9d means pounds of actual microparticle per 2000 pounds of solids present in slurry. The abbreviation for pounds of actual microparticle per 2000 pounds of solids present in slurry is xe2x80x9clbs microparticle/tonxe2x80x9d.
The microparticle is added to the papermaking furnish either before or after the flocculant is added to the furnish. The choice of whether to add the microparticle before or after the flocculant can be made by a person of ordinary skill in the art based on the requirements and specifications of the papermaking furnish.
Preferred Embodiments
The structurally rigid polymeric coagulants of this invention are prepared by condensation polymerization of one or more cyclic ditertiary amines with one or more cyclic or acyclic dihalides condensation polymerization of one or more acyclic ditertiary amines with one or more cyclic dihalides in a polar solvent such as DMF, acetonitrile, DMSO or water, or mixtures thereof. A preferred solvent is a 70:30 mixture of DMF or acetonitrile and water. Reaction temperatures can range from about ambient temperature to about 100xc2x0 C., preferably from about 40xc2x0 C. to about 60xc2x0 C. Reaction times can range from a few hours to several days, preferably from about 10 to about 24 hours.
The structurally-rigid coagulants have a molecular weight of from about 1000 to about 100,000, preferably from about 5000 to about 10,000.
In a preferred aspect of this invention, the cyclic ditertiary amine is 1,4-diazabicyclo[2.2.2]octane.
In another preferred aspect, the acyclic dihalide is 1,4-dihalobutyne or xcex1,xcex1xe2x80x2-dihalo-p-xylene.
In a more preferred aspect, the structurally rigid polymeric coagulant is poly(1,4-diazabicyclo[2.2.2]octane/1,4-dichloro-2-butyne) or poly(1,4-diazabicyclo[2.2.2]octane/xcex1,xcex1xe2x80x2-dichloro-p-xylene).
In another preferred aspect, the flocculant is poly(acrylic acid/acrylamide).
In another preferred aspect, the microparticle is colloidal borosilicate.
In another preferred aspect, the papermaking furnish is selected from fine paper, board, and newsprint papermaking furnishes.
In another preferred aspect, this invention is directed to a polymer composition comprising a condensation polymer of 1,4-diazabicyclo[2.2.2]octane and an alkynyl dihalide or an xcex1,xcex1xe2x80x2-dihalo-p-xylene.
In another preferred aspect, this invention is directed to a polymer composition comprising poly(1,4-diazabicyclo[2.2.2]octane/1,4-dichloro-2-butyne); or poly(1,4-diazabicyclo[2.2.2]octane/xcex1,xcex1xe2x80x2-dichloro-p-xylene).
In addition to the structurally rigid coagulant, the flocculant and the microparticle, additional additives such as talc, cationic starch, cationic coagulant, or mixtures thereof may be added anywhere in the system.
The appropriate dosage of structurally rigid coagulant is determined by adding different doses of the structurally rigid coagulant to a papermaking slurry either before, concurrently with, or after the addition of either a flocculant alone or a flocculant followed by a microparticle. The performance of the combined chemical additions is monitored with the focused beam reflectance microscope (FBRM) or other appropriate evaluative measurement (Britt jar, dynamic drainage analyzer, etc.). The range of doses is preferably from about 1 to about 20, more preferably from about 1 to about 8 pounds of structurally rigid coagulant/ton product.
Generally the structurally rigid coagulant is added before the flocculant and microparticle, though exceptions are practiced in the industry. When the coagulant is added before the flocculant, it is added either to the white water, the thick stock, or the thin stock. The preferred addition point is the thick stock pulp before dilution with white water.
Alternatively, the structurally rigid coagulant is added at several points in the papermaking process, including concurrently with the flocculant or microparticle.
This application results in increased cleanliness of the papermaking operation which otherwise experiences hydrophobic deposition effecting both productivity and the quality of paper.